A voice conference system for transmitting and receiving sound via a network making connection between sites has been put into practical use. The acoustic characteristic of a conference room to be used for conferences is different variously, and a conference is sometimes held in a room having a very long reverberation time. In the case that the reverberation time is long, the articulation of the sound to be emitted from a speaker deteriorates. To solve this problem, a device for suppressing the reverberation of the sound to be emitted has been proposed (Patent Document 1).
The device according to Patent Document 1 discloses that, by the operation of the key Kia corresponding to a participant Ma, the inverse filter coefficient Ga of the spatial transmission function Ha in the space ranging from the participant Ma to a microphone 31 is read from a ROM 41 and supplied to a digital filter 34i and this digital filter 34i performs inverse filter arithmetic operation in real time, thereby inversely filtering the sound signal of the participant Ma. In other words, with this device, the spatial transmission functions in the spaces ranging from the seats of respective participants Ma to Mn to a plurality of microphones 31 have been measured in advance, and the inverse filter coefficients Ga to Gn of the respective transmission functions have been stored in advance in the ROM 41.